New answers tagged subdomains
first i would read other peoples solutions in the plugin support section. next i would completely disable sef generation in settings > permalinks. last advice: do not develop on a production site, instead set up a local dev environment.
A wordpress network is exactly what you are looking for if no one needs FTP access. The only way to truly separate user info (high paranoia mode) is to have each site on a different server. Otherwise whatever information leakage that might be should be easily solvable with something that will let some of the user settings to be local to a subdomain.
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